Question: $ { \left[\begin{array}{rr}{1} & {-2} \\ {1} & {2}\end{array}\right]+\left[\begin{array}{rr}{0} & {-1} \\ {2} & {1}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{1}+{0} & {-2}+{-1} \\ {1}+{2} & {2}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{1} & {-3} \\ {3} & {3}\end{array}\right]}$